1. Field of the Invention
The present invention relates to apparatus and a method for plasma treatment of a substrate to treat such as a semiconductor wafer or the like, more specifically relates to apparatus and a method for plasma treatment of a substrate to treat by the use of plasma.
2. Description of the Related Art
So far, in apparatus for treatment of a substrate to treat such as a semiconductor wafer or the like, for instance in apparatus for plasma treatment such as plasma-etching apparatus, it is usual to dispose an annular compensation ring on a susceptor thereon the wafer W is disposed. The compensation ring is a ring that is disposed in the surroundings of the wafer to compensate characteristics of plasma generated in a treatment chamber. For instance, by means of impedance of the ring, an electric field is concentrated on the wafer to help plasma distribute intensively on the wafer. Thereby, the plasma operates intensively on the wafer disposed on the susceptor.
FIG. 14 is a vertical sectional view showing schematically the inside of the treatment chamber of typical apparatus for plasma treatment.
As shown in FIG. 14, on a susceptor 102 in a treatment chamber 101, an annular compensation ring 103 is disposed, the compensation ring 103 being constituted in a sheet of disc like member. As shown in FIG. 14, the compensation ring 103 surrounds a periphery of a wafer W disposed on the susceptor 102, being exposed to the plasma during treatment. Accordingly, a successive treatment of a plurality of wafers ensues a high temperature of the compensation ring 103. A high temperature of the compensation ring 103 affects a spatial distribution of radicals. For instance, in the etching process, a decrease of an etch rate of photo resist at a periphery of the wafer W or a difficulty in forming a contact hole is caused. In particular, when a plurality of wafers W is successively treated, there occurs a variation of the etch rates between wafers treated at an earlier turn and at a later turn.
Technology for eliminating an influence of a high temperature of a member disposed in the surroundings of a sample to plasma-treat on the plasma treatment is disclosed for instance in Japanese Patent Publication (A) No. HEI 7-310187. In the publication, apparatus in which to prevent a protector plate 6 disposed in the surroundings of a sample 2 from becoming a high temperature, the protector plate 6 and a susceptor 8 are fastened with a bolt to come into an intimate contact is proposed. Thereby, thermal conduction is improved to cool the protector plate 6. Alternatively, between a base face of the protector plate 6 and an upper face of the susceptor 8, a gas is flowed as a thermal conduction medium to help heat of the protector plate 6 diffuse easily toward the susceptor 8.
In general, when a temperature of the compensation ring 103 in the treatment chamber 101 of plasma etching apparatus 100 goes up, the etch rate shows a tendency of decreasing from a center of the wafer W toward a periphery. The situation is shown in FIG. 15 as curve 1. The tendency is in accordance with a distribution of oxygen radicals shown by curve 2 shown by a dotted line in FIG. 15.
Accordingly, in order to prevent the etch rate from decreasing at the periphery side as shown by curve 1, it is considered needs only to cool the compensation ring to lower the temperature.
However, a shape of the curve 1 that shows, over a surface direction of the wafer W, the etch rate of the wafer W plasma-etched in the treatment chamber 101 is obviously different from that of the curve 2 that shows the distribution of the oxygen radicals. That is, the curve 1 rapidly goes up at the periphery. The steepness at the periphery side of the curve 1 cannot be explained only with the distribution of the oxygen radicals.
When changing a viewpoint to pay attention to treatment gas deposit piled up at a place relatively distant from the periphery of the wafer W on the susceptor 102, one answer can be obtained. That is, when the plasma impinging against the deposit layer formed by deposition of the treatment gas, highly reactive materials such as fluorine radicals or the like are considered to produce. Curve 3 in FIG. 15 is one obtained by plotting a distribution of thus generated fluorine radicals with distance from the center of the wafer W disposed on the susceptor as abscissa. As shown by the curve 3, in accordance with the rapid rise of the curve 1 in the neighborhood of the periphery of the wafer W, in the proximity of the periphery of the wafer W, an amount of the fluorine radicals rapidly increases.
From the above, a portion from a left hand side to the center of the curve 1, that is a portion from the center toward the periphery of the wafer W reflects an influence of the oxygen radicals shown by the curve 2. A portion of a right hand side of the curve 1, that is the surroundings of the periphery of the wafer W is considered to reflect an influence of fluorine radicals of the curve 3 that is considered to generate from the deposit.
When judging from a temperature distribution point of view only, it is only needed to cool the compensation ring. However, on the other hand, when the compensation ring is cooled, the fluorine radicals generated due to plasma bombardment on the deposit that is formed by deposition of material contained in the treatment gas become to largely affect. As a result, the etch rate at the periphery of the wafer W is considered to increase rapidly. That is an antinomic problem.
The present invention is made to overcome the aforementioned problems. That is, the object of the present invention is to provide apparatus and a method for plasma treatment where even after a successive treatment of a plurality of substrates to treat, quality of the treated substrates varies less due to the turn of the treatment and the treatment can be uniformly implemented over an entire substrate to treat.